Referring to FIG. 1, an Inductive Energy Transfer System (IETS) 100 uses a magnetic field to transfer power across an air gap from a source inductor 102 to a pickup inductor 104. This system can be likened to an electrical transformer with the primary of the transformer being the source inductor and the secondary of the transformer being the pickup inductor. The primary inductor 102 is energized with an alternating current that creates a magnetic field that bridges the air (or other dielectric) gap 106 between the source (primary) inductor 102 and the pickup (secondary) inductor 104. This magnetic field induces a current in the winding of the pickup winding. The induced current is available as electric power on board a vehicle 110. This type of system allows energy to be transferred to vehicles with no physical contact between the vehicle and the wayside. The transferred energy can be used by an electrical motor 112 to provide motive power for the vehicle, charge an energy storage device 114 on board the vehicle or power auxiliary vehicle systems 116 such as HVAC, lighting systems, braking systems, controls and instrumentation.
Four basic elements are required to transfer power inductively: an AC power supply 120, a source inductor 102, a pickup inductor 104, and a controller 122 on board the vehicle to control the rate at which power is transferred to the vehicle 110. The AC power source 120 supplies current to the wayside source inductor 102. This current forms an alternating magnetic field in the air gap 106 between the wayside and pickup inductors. This field is captured by the pickup inductor 104 and induces a current in the pickup's conductors, which in turn provides electrical power to the vehicle's motor 112, battery 114, or auxiliary systems 116.
The AC power source 120 can be any AC source that can supply the required power to the wayside source inductor. The source inductor 102 consists of ferromagnetic inductor cores of the proper geometry and current carrying conductors called the primary winding. The primary winding may have various numbers of turns depending on the application.
The pickup inductor 104 is similar to the source inductor 102 but is mounted on the vehicle. The current carrying conductors of the pickup inductor are called the secondary winding and also may have various numbers of turns depending on the application. Controls 122 are required to control the power out of the pickup. This control can take the form of a resonant circuit of capacitors and the pickup. Capacitors of various values are placed in parallel with the pickup windings and solid-state switches are in series with each capacitor. Switching capacitance into or out of the circuit affects the resonant frequency of the circuit. The output current increases as the resonant frequency becomes closer to the driven (AC power) frequency. Inductive energy transfer systems for electrically powered vehicles have been the subject of previous U.S. Patents, including U.S. Pat. Nos. 3,914,562, 4,007,817, and 4,331,225, which are hereby incorporated by reference.